Thursday, December 20, 2012

Search for inborn causes has failed

Nearly all human behavior is a complex combination of nature and nuture, and people have unsupported opinions for ideological reasons. They argue that homosexuality is inborn and IQ is not. Here is an example of how leftism has corrupted a leading science journal.

Interviewer –Sarah Crespi
Wow, alright. Next up, we have a story about why homosexuality may still be around
despite the fact that it might have some evolutionary disadvantages.

Interviewee –David Grimm
Right, well that’s one of the big mysteries about homosexuality, because most homosexual people don’t procreate. The question is why and how has homosexuality, sort of, persisted in our population. We usually think, at least from a Darwinian sense, that the genes that we pass on, the traits that we pass on are adaptive. They help us become fitter; they help us produce more offspring. And homosexuality would seem to go against that, because, again, people that are homosexual tend not to have children. These researchers think they have come up with one viable explanation. ...

Well, that’s something that had been done in the past. You know, researchers have been looking for, you know, what they call a “gay gene” or “gay genes” that would help, sort of, explain the mystery. Because if there were gay genes, that could explain how it was passed down from generation to generation, and why it seemed to run more in families. But in this study, the researchers didn’t look at the genes themselves. They looked at modifications to the genes, something known as epigenetic changes, and these are chemical modifications that actually can turn certain genes on or off or modify how much of the gene is expressed in the cell, how much of the protein from that gene is made. And the researchers focused on a time when a lot of epigenetic changes are being made, namely during development in the womb, and they also looked at the interplay between hormones. Fetuses are exposed to a lot of hormones in the womb, and how that might interplay with epigenetic changes.

The interview goes on to give the impression that homosexuality is inborm, but it has no facts or papers to support the idea.

LGBT activists say that support for same-sex marriage increases when people are told that homosexual orientation has been shown to be inborn.

If an epigenetic cause to homosexuality had really been identified, that would open up the possibility of a gene therapy to change sexual orientation in adults. But the LGBT activists would find that idea offensive, so you will not hear any mention of it.

Most personality traits and other characteristics – like whether you are politically liberal or conservative or how likely you are to get a divorce – have heritability of .50; they are about 50% determined by genes. In fact, most personality traits and social attitudes follow what I call the 50-0-50 rule; roughly 50% heritable (the influence of genes), roughly 0% what behavior geneticists call “shared environment” (parenting and everything else that happens within the family to make siblings similar to each other), and roughly 50% “nonshared environment” (everything that happens outside of the family to make siblings different from each other). It turns out that parenting has very little influence on how children turn out.

There is no known behavioral trait that is 100% inborn.

Update: JayMan says All human behavioral traits are heritable. Yes, but look at his tables, and nothing is near 100%. He also says, "Third Law. A substantial portion of the variation in complex human behavioral traits is not accounted for by the effects of genes or families."